This application claims the priority right under Paris Convention of Japanese Patent Application No. Hei 11-363416 filed on Dec. 21, 1999, the entire disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a management technique of a friction coefficient based on surface roughness, an information recording medium substrate, an information recording medium and a manufacture method thereof.
2. Description of the Related Art
There is a magnetic recording medium loaded with HDD as an information recording medium. A remarkably rapid increase of a recording capacity of a hard disk drive (HDD) in recent years is realized, for one thing, by lowering (lowering glide) a gap between a magnetic head (a head) and a magnetic recording medium (a medium) during recording/reproduction (head flying height). The lowering of the gap between the head and the medium is realized by an attempt to smooth a medium surface, but the smoothed medium surface causes an adsorption problem between the head and the medium. Therefore, design of the medium surface is always troubled with trade-off between the lowering of glide and avoiding of head adsorption.
In order to solve mutually contradictory problems of the smoothing of the medium surface required for the lowered glide, and the avoiding of an adsorption tendency accompanied by the smoothing (=tendency of increase of a friction coefficient), a precision surface design is necessary.
For shape management of the medium surface, from a point of view that process feedback is easy, surface roughness parameters such as Rmax and Ra by an atomic force microscope (AFM), normalized roughness Ra/Rmax, and the like have heretofore been used.
Herein, Ra and Rmax are defined by the Japanese Industrial Standard (JIS B0601). Rmax is the above-mentioned maximum height (the distance from a highest peak to a lowest valley), Ra is the above-mentioned center-line-mean roughness (the average of an absolute value of a deviation from a center line of a roughness curve to the roughness curve.
However, by checking a relation between Rmax, Ra or Ra/Rmax measured by AFM and the friction coefficient, it has been found that in a low glide area (about 10 nm or less) requiring more precise surface design, such surface management technique is extremely bad in sensitivity. FIGS. 1 and 2 show the relation between the substrate surface roughness (Rmax (FIG. 1), Ra (FIG. 2)) measured by AFM and the friction coefficient. Even in the same Rmax (e.g. Rmax of about 7.5 nm) and the friction coefficient with a range of 0.7 to 2.2, and it is thus impossible to manage the friction coefficient with the parameters such as Rmax and Ra.
On the other hand, there is proposed a technique of taking a correlation between a bearing area (bearing ratio) and the friction coefficient to manage the friction coefficient. Specifically, in a magnetic recording medium constituted by forming texture on a medium surface, there is proposed a technique of forming the texture (concave/convex) in such a manner that the bearing area in a depth of 20 nm from a surface top portion is 20% or less, and defining the friction coefficient to be small (Japanese Patent Application Laid-Open No. 189756/1993). Additionally, the bearing area means a proportion occupied by an area appearing when the concave/convex in a measured area is cut on an arbitrary equal height surface (horizontal surface) in the measured area, and can be measured using the atomic force microscope (AFM) or the like.
However, the technique principally aims at the magnetic recording medium formed by polishing an aluminum alloy substrate surface with an NiP film formed thereon with a free abrasive grain and performing a texture processing, and uses the bearing area in the depth of 20 nm from the surface top portion as the parameter (i.e., a rough magnetic recording medium with a surface roughness of 20 nm or more is an object). Therefore, there is a problem that with respect to the magnetic recording medium having a surface roughness of Rmax 15 nm or less, the technique is completely useless as a friction coefficient management technique.
Additionally, the technique is derived from an experiment, and is not derived based on theories such as a real contact area described later.
Furthermore, for example, when a texture forming method differs, the total number of protrusions, protrusion mode (protrusion curvature radius or horizontal sectional shape, protrusion height), and the like differ. Even with the same Rmax or Ra, the friction coefficient by the medium surface differs. Therefore, in this case, the aforementioned technique is completely useless as the management technique of the friction coefficient of the medium surface.
The present invention has been developed under the aforementioned background, and an object thereof is to provide an inventive surface management technique in which a precise surface design is obtained even in a low glide area of about 10 nm or less, substrate for an information recording medium (substrate for a magnetic recording medium) designed by the surface management technique, an information recording medium (a magnetic recording medium) and a manufacture method thereof.
As a result of intensive researches on a friction force acting on a magnetic head, the present inventors have found the following.
The friction force acting on the magnetic head can be represented by the following equation (1) because a lubricant and moisture in air usually exist on a contact surface.
F=xcexcN+F1+F2+F3+xe2x80x83xe2x80x83(1)
In the above equation (1), F is a friction force, xcexc is a coefficient static friction, N is a normal force, F1 is a meniscus force by the lubricant, F2 is a meniscus force of the moisture, and F3 is a cohesive force by other materials (organic contaminant, and the like). In a contact surface of the surface of a head (or a pad of a padded slider for a purpose of reducing a contact area with a magnetic disk) with a medium surface having a certain surface roughness, since there is a concave/convex on the medium surface, as compared with an apparent contact area, a real contact area is extremely small. When a head load is added, by a pressure concentrated on a convex portion vertex, the convex portion vertex is crushed, the real contact area increases, and the friction force increases. However, there is no change in the apparent contact area. Since stiction (cohesion) of contacted surfaces occurs in the real contact surface, with increase of the real contact area, a large force (a force for cutting off the friction force) is necessary for separating (shearing) the cohesion surfaces. Therefore, it can be said that xcexcN xe2x88x9d the real contact area.
Therefore, from a standpoint of surface design, it is assumed that when a shape parameter representative of the real contact area between the magnetic head and the medium is extracted, an indication sensitive to friction is theoretically obtained.
When the surface roughness obtained by precisely polishing a glass substrate surface is Rmax 15 nm or less, the real contact area between the magnetic head and the medium is proportional to the total number of protrusions able to contact the head (FIG. 9). By checking a relation between the total number of protrusions present in a predetermined depth of 4 nm from a maximum protrusion height in a 5 xcexcm square (5 xcexcm*5 xcexcm) AFM image and the friction coefficient, it has been found that the friction coefficient depends on (is proportional to) the total number of protrusions (protrusion density) in the predetermined depth. Additionally, since a certain degree of time is necessary for calculation of the protrusion density from AFM data, it cannot be said that process feedback is easy, and this is not a suitable parameter for process monitor. Therefore, it has been studied whether or not the protrusion density in the predetermined depth can directly be represented by some AFM measured value. Specifically, for example, by checking a relation between a bearing area in a depth position of 4 nm from the maximum protrusion height (Rmax) in the 5 xcexcm square AFM image and the total number of protrusions in the same depth position, it has been found that the bearing area of the predetermined depth position is in a proportional relation to the protrusion density in the predetermined depth. Furthermore, by checking a relation between the bearing area of the depth position of 4 nm from the maximum protrusion height (Rmax) in the 5 xcexcm square AFM image and the friction coefficient, a relation of FIG. 10 has been obtained, and it has been found that the bearing area of the predetermined depth position is in a correlation with the friction coefficient. The bearing area of the predetermined depth position is easily obtained as an AFM measurement result, the process feedback is easy, and the area is a parameter suitable for the process monitor.
As described above, it has been found that, for example, by using the bearing area in the vicinity of the depth of 4 nm from the maximum protrusion height (Rmax) as the shape parameter representative of the real contact area, with respect to a magnetic recording medium having surface roughness of Rmax 15 nm or less, the friction coefficient can be managed.
However, when the bearing area is measured by AFM, there is a capability (measurement error) measurement in AFM itself. Moreover, by the presence of an abnormal protrusion (irregular point), such as dust, which fails to influence a glide height or the friction coefficient, the AFM measurement error is sometimes generated. Because of the error, Rmax by AFM measurement does not represent a real peak height. The error is usually of the order of 1 to 2 nm, and largely influences the magnetic recording medium having the surface roughness (texture) of Rmax 15 nm or less. Particularly, with respect to the magnetic recording medium having the surface roughness (texture) of Rmax 10 nm or less, the influence of the error of 1 to 2 nm is remarkably large. For example, when the maximum protrusion height deviates by 1 to 2 nm, a slice level also deviates by 1 to 2 nm, and it is sometimes impossible to manage the friction coefficient in the bearing area corresponding to the slice level. Even in a case in which the management is possible, for the magnetic recording medium friction coefficient managed by the bearing area, since the slice level is disordered (is not optimum), the error is large, and it has been found that the friction coefficient management technique is insufficient.
Moreover, as a result of further researches, it has been found that when a bearing curve is repeatedly measured by AFM, by obtaining a bearing area value with a bearing height measured value rapidly starting to scatter in the vicinity of the maximum protrusion height (BA=0%), and utilizing various AFM measured values excluding data from BA=0% to the bearing area value with the bearing height measured value rapidly starting to scatter, the AFM measurement scattering problem can be solved.
For example, when the repeated measurement of the bearing curve is performed with respect to the surface having a surface roughness Rmax of about 15 nm or less by the atomic force microscope (AFM), in the vicinity of the maximum protrusion height (BA=0%), the bearing area value is obtained at which the measured value of the bearing height rapidly starts to scatter (0.5% in FIG. 7), and the corresponding bearing height (real peak height) is obtained from the bearing curve (FIG. 8). A correlation of the bearing area in the predetermined depth (3 nm in FIG. 8) from the real peak, that is, the bearing area (offset bearing area: OBA %) when the slice level is offset (subtracted) with the friction coefficient of the medium surface is checked by changing the predetermined depth, and from this correlation, with respect to a friction coefficient change amount, a predetermined depth (predetermined slice level) is obtained at which the corresponding bearing area change amount increases. It has been found that the friction coefficient based on the surface roughness can be managed with good precision by performing management of the friction coefficient based on the correlation (e.g., FIG. 5) of the bearing area value (offset bearing area value) in the predetermined slice level with the friction coefficient.
In this manner, by employing OBA % as the indication sensitive to friction, and employing the OBA % as a process monitor indication, the friction coefficient based on the surface roughness can be managed with good precision.
Moreover, in the medium surface design, by beforehand obtaining a correlation of forming conditions for forming a certain medium surface state (total number of protrusions, curvature, and the like) with OBA %, via the correlation between OBA % and friction coefficient, the friction coefficient based on the surface roughness can be designed with good precision, and a magnetic recording medium having a desired friction coefficient can be obtained by selecting the forming conditions.
The present invention is provided with the following constitutions.
(Constitution 1) An information recording medium substrate having a surface roughness of Rmax 15 nm or less, wherein for a substrate surface, a bearing area value (offset bearing area value) in a depth of 0.5 to 5 nm (predetermined slice level) from a bearing height (real peak height) corresponding to the bearing area value of 0.2% to 1.0% is 90% or less.
(Constitution 2) An information recording medium substrate having a surface roughness of Rmax 15 nm or less, wherein for a substrate surface, when a depth corresponds to 20 to 45% of Rmax from a bearing height (real peak height) corresponding to a bearing area value of 0.2% to 1.0% is set as a slice level, the bearing area value (offset bearing area value) is 90% or less.
(Constitution 3) The information recording medium substrate according to constitution 1 or 2 wherein the information recording medium substrate is a glass substrate whose surface is subjected to precision polishing and/or etching treatment.
(Constitution 4) An information recording medium having a surface roughness of Rmax 15 nm or less on a medium surface, wherein for a medium surface of the information recording medium, a bearing area value (offset bearing area value) in a depth of 0.5 to 5 nm (predetermined slice level) from a bearing height (real peak height) corresponding to the bearing area value of 0.2% to 1.0% is 90% or less.
(Constitution 5) An information recording medium having a surface roughness of Rmax 15 nm or less on a medium surface, wherein for a medium surface of the magnetic recording medium, when a depth corresponds to 20 to 45% of Rmax from a bearing height (real peak height) corresponding to a bearing area value of 0.2% to 1.0% is set as a slice level, the bearing area value (offset bearing area value) is 90% or less.
(Constitution 6) The information recording medium according to constitution 4 or 5 wherein a friction coefficient based on the surface roughness of the medium surface is 3 or less.
(Constitution 7) The information recording medium according to constitutions 4 to 6 wherein a correlation of the friction coefficient in the information recording medium with various lubricants formed thereon with an offset bearing area is checked, and the lubricant with a reduced friction force by the lubricant is employed.
(Constitution 8) The information recording medium according to constitution 7 wherein the lubricant is a lubricant classified in perfluoro alkyl polyether (PFPE), including ether joining in a main chain, having xe2x80x94(OCF2F2)m(OCF2)nxe2x80x94 straight chain structure, and having a hydroxyl group as a terminal group.
(Constitution 9) A manufacture method of a glass substrate for an information recording medium, comprising steps of: immersing the glass substrate in a heated chemical reinforcing treatment liquid, and subjecting an ion on a glass substrate surface layer to ion exchange with an ion in the chemical reinforcing treatment liquid to chemically reinforce the glass substrate; and treating the surface of the glass substrate drawn up from the chemical reinforcing treatment liquid with a treatment liquid containing silicofluoric acid.
(Constitution 10) A manufacture method of a glass substrate for an information recording medium, provided with steps of: polishing a glass substrate surface; and immersing the glass substrate in a heated chemical reinforcing treatment liquid, and subjecting an ion of a glass substrate surface layer to ion exchange with an ion in the chemical reinforcing treatment liquid to chemically reinforce the glass substrate, the method comprising steps of: controlling the glass substrate surface by a chemical treatment to provide a desired surface roughness before the chemical reinforcing step; and treating the surface of the glass substrate drawn up from the chemical reinforcing treatment liquid with a treatment liquid containing silicofluoric acid.
(Constitution 11) The manufacture method of the glass substrate for the information recording medium according to constitution 10 wherein the chemical treatment comprises treatment with the treatment liquid containing at least one acid selected from the group consisting of sulfuric acid, phosphoric acid, nitric acid, hydrofluoric acid, and silicofluoric acid, or alkali.
(Constitution 12) The manufacture method of the glass substrate for the information recording medium according to any one of constitutions 9 to 11 wherein a concentration of the silicofluoric acid is in a range of 0.01 to 10 wt %.
(Constitution 13) A manufacture method of an information recording medium, comprising steps of forming at least a recording layer on the surface of the information recording medium glass substrate obtained by constitutions 9 to 12.
(Constitution 14) A management technique of a friction coefficient based on a surface roughness in an information recording medium surface having a surface roughness of Rmax 15 nm or less, comprising steps of: when repeated measurement of a bearing curve is performed by an atomic force microscope (AFM), obtaining a bearing area value at which a measured value of a bearing height rapidly starts to scatter in the vicinity of a maximum protrusion height (BA=0%), and obtaining the bearing height (real peak height) corresponding to the bearing area value from the bearing curve; checking a correlation of a bearing area in a predetermined depth from the real peak height with the friction coefficient based on the surface roughness by changing the predetermined depth; from the correlation, with respect to a change amount of the friction coefficient, obtaining a predetermined depth (predetermined slice level) at which the corresponding change amount of the bearing area increases; and using the bearing area value (offset bearing area value) in the predetermined slice level to manage the friction coefficient based on the surface roughness.
(Constitution 15) A management technique of a friction coefficient based on a surface roughness in an information recording medium having a surface roughness of Rmax 15 nm or less on a medium surface, comprising steps of: using a bearing area in a depth of 0.5 to 7 nm (slice level) from a maximum height (Rmax) by AFM measurement to manage the friction coefficient based on the surface roughness.
(Constitution 16) A management technique of a friction coefficient based on a surface roughness in an information recording medium having a surface roughness of Rmax 15 nm or less on a medium surface, comprising steps of: using a bearing area when a depth corresponds to 20 to 40% of Rmax from a maximum height (Rmax) by AFM measurement is set as a slice level, and managing the friction coefficient based on the surface roughness.
(Constitution 17) An information recording medium manufacture method for manufacturing an information recording medium having a desired medium surface based on the management technique of the friction coefficient based on the surface roughness according to constitutions 14 to 16.
(Constitution 18) A manufacture method of an information recording medium substrate for reflecting an information recording medium substrate surface in an information recording medium surface to obtain a desired medium surface, the method comprising steps of manufacturing the information recording medium substrate having a desired substrate surface based on the management technique of the friction coefficient based on the surface roughness according to constitutions 14 to 16.
(Constitution 19) A management technique of a surface state of an information recording medium substrate surface having a surface roughness of Rmax 15 nm or less, the technique comprising steps of: when repeated measurement of a bearing curve is performed by an atomic force microscope (AFM), obtaining a bearing area value at which a measured value of a bearing height rapidly starts to scatter in the vicinity of a maximum protrusion height (BA=0%); and utilizing various AFM measured values excluding data from BA=0% to the bearing area value at which the bearing height measured value rapidly starts to scatter.
(Constitution 20) An information recording medium substrate manufacture method for manufacturing an information recording medium substrate having a desired substrate surface based on the surface state management technique of constitution 19.
(Constitution 21) A management technique of a surface state of an information recording medium surface having a surface roughness of Rmax 15 nm or less, the technique comprising steps of: when repeated measurement of a bearing curve is performed by an atomic force microscope (AFM), obtaining a bearing area value at which a measured value of a bearing height rapidly starts to scatter in the vicinity of a maximum protrusion height (BA=0%); and utilizing various AFM measured values excluding data from BA=0% to the bearing area value at which the bearing height measured value rapidly starts to scatter.
(Constitution 22) An information recording medium manufacture method for manufacturing an information recording medium having a desired medium surface based on the surface state management technique of constitution 21.
According to the constitution 1, with respect to the surface of the information (magnetic) recording medium substrate, in the method described in constitution 14 described later, by obtaining, from an experiment, the bearing area value of 0.2% to 1.0% at which the bearing height measured value rapidly starts to scatter, further obtaining the depth of 0.5 to 5 nm from the real peak height as the slice level, and defining the bearing area value (offset bearing area value: OBA %) in the slice level to 90% or less to form the information (magnetic) recording medium, the information (magnetic) recording medium whose friction coefficient based on the surface roughness is small (usually, 3 or less) is obtained.
Moreover, like the constitution 2, by setting the depth of the slice level in the constitution 1 to the depth of slice level corresponds to 20 to 45% of Rmax, and defining the bearing area value (offset bearing area value: OBA %) in the slice level to 90% or less to form the information (magnetic) recording medium, the information (magnetic) recording medium whose friction coefficient based on the surface roughness is small (usually 3 or less) is obtained.
Particularly, the constitutions 1, 2 are suitable for the substrate in which the surface roughness of the information (magnetic) recording medium substrate is Rmax 10 nm or less.
Additionally, in the information (magnetic) recording medium substrate with surface roughness Rmax of around 10 to 11 nm, for example, it is preferable that the slice level is 4 nm (36 to 40% of Rmax), OBA % is 70% or less. In the magnetic recording medium substrate with Rmax of around 7 to 8 nm, for example, it is preferable that the slice level is 3 nm (38 to 43% of Rmax) and OBA % is 90% or less (preferably 40%xc2x120% (20 to 60%) with a CSS system information (magnetic) recording medium substrate and preferably 70%xc2x120% (50 to 90%) with a load/unload system information (magnetic) recording medium substrate). In the information (magnetic) recording medium substrate with Rmax of around 5 to 6 nm, for example, it is preferable that the slice level is 1.5 to 2 nm (25 to 40% of Rmax) and OBA % is 80% or less (preferably 60%xc2x120% (40 to 80%) with the load/unload system information (magnetic) recording medium substrate). Moreover, in the information (magnetic) recording medium substrate with Rmax of 3 nm or less, in which the substrate surface is super-smooth, for example, it is preferable that the slice level is 0.5 to 1.3 nm (20 to 43% of Rmax) and OBA % is 90% or less (preferably 70%xc2x120% (50 to 90%) with the load/unload system information (magnetic) recording medium substrate).
Additionally, the bearing area value at which the measured value of the bearing height rapidly starts to scatter may be of the order of 0.5%, specifically in a range of 0.2 to 1.0%, preferably 0.3 to 0.7%, more preferably 0.4 to 0.6%.
According to the constitution 3, when the information (magnetic) recording medium substrate is a glass substrate with the surface subjected to precision polishing and/or etching treatment, and therefore the magnetic recording medium substrate according to the constitution 1 or 2 is securely and easily obtained. As the concrete manufacture method of etching treatment, means of the constitutions 9 to 12 described later are exemplified.
According to the constitutions 4, 5, similarly as the constitutions 1, 2, obtained is the information (magnetic) recording medium which has the surface roughness of Rmax 15 nm or less on the medium surface and in which the friction coefficient based on the surface roughness of the medium surface is small (usually 3 or less).
Particularly, the constitution 4, 5 are suitable for the information (magnetic) recording medium in which the surface roughness of the information (magnetic) recording medium surface is Rmax 10 nm or less.
Additionally, in the information (magnetic) recording medium in which the surface roughness of the medium surface is Rmax of around 10 to 11 nm, for example, it is preferable that the slice level is 4 nm (36 to 40% of Rmax) and OBA % is 70% or less. In the information (magnetic) recording medium with Rmax of around 7 to 8 nm, for example, it is preferable that the slice level is 3 nm (38 to 43% of Rmax) and OBA % is 90% or less (preferably 40%xc2x120% (20 to 60%) with the CSS system information (magnetic) recording medium, and preferably 70%xc2x120% (50 to 90%) with the load/unload system information (magnetic) recording medium). In the information (magnetic) recording medium with Rmax of around 5 to 6 nm, for example, it is preferable that the slice level is 1.5 to 2 nm (25 to 40% of Rmax) and OBA % is 80% or less (preferably 60%xc2x120% (40 to 80%) with the load/unload system information (magnetic) recording medium). Moreover, in the information (magnetic) recording medium with Rmax of 3 nm or less, in which the medium surface is super-smooth, for example, it is preferable that the slice level is 0.5 to 1.3 nm (20 to 43% of Rmax) and OBA % is 90% or less (preferably 70%xc2x120% (50 to 90%) with the load/unload system information (magnetic) recording medium).
Additionally, the bearing area value at which the bearing height measured value rapidly starts to scatter may be of the order of 0.5%, specifically in a range of 0.2 to 1.0%, preferably 0.3 to 0.7%, more preferably 0.4 to 0.6%.
In order to obtain the medium surface of the constitutions 4 to 6, there are: a method of controlling the surface state of the medium surface in accordance with the substrate surface like the constitutions 1 to 3, and forming an underlayer, recording (magnetic) layer, protective layer, and lubricant layer on the substrate surface to obtain the desired medium surface; a method of controlling the surface state of any layer formed on the substrate to obtain the desired medium surface; and the like. As the method of controlling the surface state, a mechanical treatment, chemical treatment, growth of a crystal grain by sputtering, optical treatment by laser light, and the like are exemplified.
Additionally, by using the information (magnetic) recording medium glass substrate obtained by subjecting the surface of the constitution 3 to the precision polishing and/or the etching treatment, the information (magnetic) recording medium according to the constitutions 4 to 6 is securely, easily and preferably obtained. Moreover, since it is unnecessary to dispose a layer for controlling the surface state of the medium surface between the recording (magnetic) layer and the magnetic head, spacing (flying height) between the information (magnetic) recording medium and the magnetic head is reduced, and high recording density reproduction is preferably enabled.
According to the constitution 6, by defining the friction coefficient based on the surface roughness of the medium surface to 3 or less, the information (magnetic) recording medium is securely obtained in which the friction coefficient based on the surface roughness is 3 or less. The friction coefficient is preferably 2 or less, more preferably 1.5 or less.
According to the constitution 7, by checking the correlation of the friction coefficient in the information (magnetic) recording medium with various lubricants formed thereon with the offset bearing area, the lubricant with the reduced friction force by the lubricant can be selected.
Additionally, needless to say, by using the management technique of the friction coefficient based on the surface roughness according to the constitutions 14 to 16, forming the lubricant on the surface, and similarly performing evaluation, the lubricant with the reduced friction force by the lubricant can be selected.
According to the constitution 8, by using the lubricant classified in perfluoro alkyl polyether (PFPE), including ether joining in the main chain, having xe2x80x94(OCF2F2)m(OCF2)nxe2x80x94 straight chain structure, and having the hydroxyl group as the terminal group, the friction force by the lubricant can securely be reduced.
The constitutions 9 to 14 are concrete methods for obtaining the information (magnetic) recording medium substrates of the constitutions 1 to 3, and the information (magnetic) recording mediums of the constitutions 4 to 8. Additionally, the information (magnetic) recording medium substrates of the constitutions 1 to 3, and the information (magnetic) recording mediums of the constitutions 4 to 8 are not limited by the following manufacture methods.
According to the constitution 9, by performing the steps of: immersing the glass substrate in the heated chemical reinforcing treatment liquid, and subjecting the ion of the glass substrate surface layer to ion exchange with the ion in the chemical reinforcing treatment liquid to chemically reinforce the glass substrate; and treating the surface of the glass substrate drawn up from the chemical reinforcing treatment liquid with the treatment liquid containing silicofluoric acid, a surface roughness scattering is suppressed, and it is possible to accurately control OBA %. By elucidating causes of the measurement scattering of AFM itself during measurement of the bearing area by AFM (the measurement error from abnormal protrusion which supposedly fails to influence the glide height or the friction coefficient) with respect to the chemical reinforcing glass substrate, it has been found that many abnormal protrusions as the causes of the measurement scattering are generated in the chemical reinforcing treatment step, or that the surface roughness increases by the chemical reinforcing treatment step after the precision polishing. Moreover, it has been considered that by suppressing the causes of the measurement scattering, the OBA % can accurately be controlled. For a treatment after the chemical reinforcing treatment, there is a method of cleaning the glass substrate surface with the chemical treatment liquid, and as the chemical treatment liquid, the treatment liquid containing silicofluoric acid is preferable rather than the treatment liquid containing sulfuric acid. This is because with sulfuric acid treatment, scattering is produced in a value of OBA %. By performing the silicofluoric acid treatment as the treatment after the chemical reinforcing treatment, the abnormal protrusion as the cause of the measurement scattering is removed, and it is possible to strictly control OBA %.
Moreover, like the constitution 10, it is preferable to control the glass substrate surface by the chemical treatment and provide the desired surface roughness before the chemical reinforcing step. If the chemical treatment (excluding silicofluoric acid) for the control to obtain the desired surface roughness is performed after the chemical reinforcing treatment, a change is brought about in the chemical reinforcing layer (compression stress layer, pulling stress layer), and deterioration of flatness of the substrate is unfavorably caused.
Like the constitution 11, the chemical treatment is performed with the treatment liquid containing at least one acid selected from sulfuric acid, phosphoric acid, nitric acid, hydrofluoric acid, and silicofluoric acid, or alkali. Concentration, treatment temperature, and treatment time of these acids and alkali are appropriately adjusted in accordance with the substrate surface state to be obtained.
Like the constitution 12, the concentration of silicofluoric acid for the silicofluoric acid treatment after the chemical reinforcing treatment is preferably in a range of 0.01 to 10 wt %. When the concentration is less than 0.01 wt %, the abnormal protrusion as the cause of the AFM measurement scattering unfavorably fails to be securely removed in some case. With the concentration exceeding 10 wt %, the glass substrate surface is etched, the surface state of the substrate surface formed by chemical treatment before the chemical reinforcing treatment changes, and the surface roughness unfavorably increases. The concentration is preferably 0.05 to 7 wt %, more preferably 0.1 to 5 wt % in respect of controlling property.
Moreover, like the constitution 13, by forming at least a recording (magnetic) layer on the surface of the recording (magnetic) recording medium glass substrate obtained by the constitutions 9 to 12, the information (magnetic) recording medium provided with the desired friction coefficient can be obtained. A magnetic layer material in the present invention is not particularly limited. A known magnetic layer material can be used. Moreover, besides the magnetic layer, it is also possible to form an underlayer for controlling a crystal orientation of the magnetic layer to enhance a magnetic characteristic, a protective layer for enhancing anticorrosion and mechanical durability of the magnetic recording medium, a lubricant layer for adjusting the friction coefficient, a seed layer for controlling crystal grain diameter and grain diameter distribution of the underlayer and magnetic layer, and the like. Also for the seed layer, underlayer, protective layer, and lubricant layer, known materials can be used.
According to the constitution 14, since the correlation of the offset bearing area with the friction coefficient (e.g., FIG. 5) is in a proportional relation and a correlation high in sensitivity, the friction coefficient based on the surface roughness in the information (magnetic) recording medium surface can be designed or managed with good precision using the offset bearing area.
Particularly, when the friction coefficient based on the medium surface roughness of the information (magnetic) recording medium is managed, the constitution 14 can be applied to the surface roughness management of the information (magnetic) recording medium substrate and information (magnetic) recording medium, and is suitable for the surfaces having the surface roughness of Rmax 15 nm or less, and further Rmax 10 nm or less.
By using the bearing area in the depth of 0.5 to 7 nm (slice level) from the maximum protrusion height (Rmax) according to the constitution 15, or using the bearing area when the depth corresponds to 20 to 40% of Rmax from the maximum protrusion height (Rmax) is set as the slice level according to the constitution 16, and managing the friction coefficient based on the surface roughness, even with the influence of the AFM measurement scattering, it is possible to substantially design or manage the friction coefficient based on the surface roughness.
According to the constitution 17, by manufacturing the information (magnetic) recording medium having the desired medium surface based on the management technique of the friction coefficient based on the surface roughness of the constitutions 14 to 16, the information (magnetic) recording medium having the desired friction coefficient can be obtained. As the method of obtaining the information (magnetic) recording medium having the desired medium surface, there are: a method of controlling the surface state of the medium surface in accordance with the substrate surface, and forming the underlayer, recording (magnetic) layer, protective layer, and lubricant layer on the substrate surface to obtain the desired medium surface; a method of controlling the surface state of any layer formed on the substrate to obtain the desired medium surface; and the like.
Particularly, in order to reduce the spacing (flying height) between the information (magnetic) recording medium and the magnetic head to enable the high recording density reproduction, it is preferable to control the substrate surface. Like the constitution 18, the present invention is preferably applied to the manufacture method of the information (magnetic) recording medium substrate having the desired substrate surface based on the management technique of the friction coefficient based on the surface roughness of the constitutions 14 to 16.
According to the constitutions 19 or 21, as the management technique of the surface states of the information (magnetic) recording medium substrate and information (magnetic) recording medium, by utilizing various AFM measured values excluding data from BA=0% to the bearing area value at which the bearing height measured value rapidly starts to scatter, the AFM measurement scattering problem can be solved. For example, when OBA % is used, the influence of the AFM measurement error is hardly exerted, and the friction coefficient based on the surface roughness can be designed or managed with good precision.
Additionally, various AFM measured values referred to in the constitution 19 or 21 include not only the offset bearing area (OBA %), but also Rmax, Ra, Ra/Rmax, bearing area (BA %), and the like.
Moreover, for example, by excluding the data with scattering measured values from the AFM measured data, and using the data after the exclusion to obtain the bearing curve, Rmax, Ra, Ra/Rmax, BA %, and the like, the influence of AFM measurement error can be removed, and accurate data can be obtained. These operations can easily be performed by settings in an AFM measurement apparatus.
Like the constitution 20, by applying the present invention to the manufacture method of the information (magnetic) recording medium substrate having the desired substrate surface based on the management technique of the surface state of the constitution 19, the information (magnetic) recording medium substrate for obtaining the information (magnetic) recording medium having the desired friction coefficient can be obtained.
Moreover, like the constitution 22, by applying the present invention to the manufacture method of the information (magnetic) recording medium having the desired medium surface based on the surface state management technique of the constitution 21, the information (magnetic) recording medium having the desired friction coefficient can be obtained.